This invention relates to internal combustion engines which have one or more power pistons that reciprocate in one or more cylinders. In particular, the invention relates to engines of this type which operate on a four stroke cycle in which the power pistons cyclically undergo fuel inlet strokes, compression strokes, expansion strokes and exhaust strokes. More particularly, the invention relates to inlet valves and valve operating components which admit a fuel and air mixture into the cylinders of engines of this type.
Fuel efficiency may be defined as pounds of fuel consumed per horsepower hour of work delivered. The fuel efficiency of most engines of the above identified type varies greatly as a function of power output or engine speed. Efficiency is highest when the engine is operating at or near its full power output and at a steady speed. Efficiency decreases when the engine is operated at reduced power outputs. Many uses of such engines require that power output be reduced much of the time. This is most notably the case with automobile engines. Automobile engines are designed to provide for occasional periods of high power output. This is needed, for example, to accelerate the vehicle on freeway on-ramps or while passing other vehicles or to maintain speed on an upgrade. Power output is reduced when the vehicle is cruising at a steady speed on a freeway or highway or is slowed by traffic conditions. Power output ceases when the vehicle is temporarily stopped with the engine idling.
The practical result of these factors is that most conventional automobile engines operate with reduced fuel efficiency much of the time. This increases operating cost, unproductively consumes fuel resources and has adverse effects on efforts to reduce emission of pollutants into the environment.
This problem arises in part as the typical automobile engine is designed to have a low compression ratio that provides for optimum performance when the engine operates at or near full power output. A higher compression ratio would provide greater efficiency during the periods when the engine is being operated at reduced power output but, in the conventional engine, the high ratio causes overly rapid fuel burning resulting in detonation or xe2x80x9cknockingxe2x80x9d at times when the engine must be operated at or near maximum power output. Fuel detonation severely strains engine components, creates unacceptable noise and drastically reduces engine efficiency.
It has heretofore been recognized that more efficient overall operation can be realized by designing the engine to have a compression ratio which varies as a function of engine load. Compression ratio can be high when the load is light as detonation is not a problem under that condition. In engines which operate on the Atkinson cycle, a mechanism is provided which varies the length of travel of the power pistons in the cylinders so that the inlet stroke is much shorter than the power or expansion stroke. Some prior engines have auxiliary pistons which reciprocate in chambers that are communicated with the power piston cylinders. Auxiliary piston movement varies the compression ratio in, response to changes of engine load. The auxiliary pistons take up a substantial amount of space in the combustion chambers. This requires that the inlet and exhaust valves be smaller than would be desirable for optimum breathing capacity. Engines of these prior kinds require bulky additional components which substantially complicate the engine and which are very prone to rapid wearing.
Engines of the Miller cycle type also vary the compression ratio as a function of power output and are not subject to the above described problems. In a Miller cycle engine the effective volume of the cylinders is varied by varying the timing of closing of the fuel inlet valves relative to power piston position. For example, closing of the fuel inlet valve may be delayed until after the intake stroke of the piston is completed and the subsequent compression stroke is underway. Thus actual compression of the fuel charge does not begin until some time after the compression stroke movement of the piston has commenced. This decreases compression ratio by an amount that is determined by the timing of the delay of closing of the fuel inlet valves. The inlet valve actuating mechanism increases the delay when engine power output is increased and decreases the delay when power output is reduced and thereby varies compression ratio as needed to provide for more efficient operation throughout the range of power outputs.
The above described mode of operation of prior Miller cycle engines requires the effective size of the combustion chamber to be relatively small. Consequently, a relatively small charge of fuel is compressed to normally high pressure at the time that combustion begins. The following power stroke utilizes the full cylinder volume. This results in a very high expansion ratio during the power stroke enabling the engine to extract more work from a given charge of fuel. This advantage has not heretofore resulted in extensive use of Miller cycle engines in automobiles as the low effective size of the combustion chamber, relative to cylinder volume, causes the prior engines to have a low power output per liter of piston displacement.
The fuel inlet valves and valve operating mechanism of prior Miller cycle engines are not designed to resolve other problems which also adversely affect fuel efficiency. For example, the operator controls the speed and power output of a conventional engine with a throttle valve which is situated in the flow path of the air and fuel. The engine must expend power in order to draw the mixture through the flow path constriction formed by the throttle valve. This throttling toss is a function of the product of the flow rate through the throttle valve and the pressure difference between the upstream and downstream side of the valve. Throttling loss is minimal when the engine operates at maximum power as the pressure difference across the fully open valve is minimal. The throttling loss is also minimal when the engine is operating at or near idling speed as the flow rate through the valve is minimal at that time. Throttle loss rises substantially and may consume as much as 30% of the engine power at the intermediate region of the engines output power range. As has been pointed out above, automobile engines operate within this intermediate power region much of the time. Elimination of the throttle and its attendant losses would substantially increase fuel efficiency of the engine.
The fuel inlet valves of prior engines create significant additional throttling loss. This is particularly pronounced when the inlet valves are spring biased poppet valves such as are present in modern engines. Poppet valves create a very substantial constriction in the fuel and air mixture flow path at the initial stage of opening of the valve and at the final stage of closing of the valve. Opening of the poppet valve is undesirably gradual as it is momentarily stationary at the start of the opening stage. Closing of the valve is also undesirably gradual as it must be brought to a stationary condition during that period. Reduction of this additional throttling loss at the inlet valve would further enhance fuel efficiency of the engine.
Most engines are designed to produce what is known as the squish effect during the final stage of the compression strokes of the pistons. The spark plug extends into a more or less centered recess in the cylinder head surface which forms the top of the combustion chamber. Other portions of the cylinder head surface, termed squish areas, are very closely approached by the power piston as it reaches top dead center position. This speeds the fuel combustion process by driving highly compressed and heated fuel and air mixture towards the spark plug with a rapid and turbulent motion. Hastening the combustion process enhances power output and output and increases fuel efficiency by avoiding fuel detonation. Detonation occurs when an unburned portion of highly compressed fuel charge reaches the the ignition temperature. A violent total combustion of the fuel charge takes place instantaneously creating an audible xe2x80x9cknockxe2x80x9d. Loss of power, overheating, and engine damage may follow.
Conventional engines have a smaller squish area then would be desirable at low and intermediate loads in order to avoid combustion rumble at high loads. Combustion rumble occurs when the fuel charge burns too fast and differs from detonation in that the burning is not instantaneous. However, it is fast enough to impose excessive loads on the engine bearings and gas turbulence is so great as to transfer too much heat to the cooling system. The transferred heat is lost energy which cannot be converted to useful work in the expansion process.
The present invention is directed to overcoming problems discussed above.
In one aspect the present invention provides a fuel inlet valve system for an internal combustion engine that has at least one power piston which reciprocates within an engine cylinder. The fuel inlet valve system includes a fuel inlet valve having a sleeve with an outlet end that opens into the engine cylinder and having at least one fuel inlet port in a sidewall of the sleeve. A valve piston is movable along a path of travel which extends axially within the sleeve, the valve piston being movable away from the outlet end of the sleeve through open positions at which the inlet port is increasingly communicated with the outlet end and being movable towards the outlet end into closed positions at which fuel flow from the inlet port to the outlet end is blocked by the valve piston. A valve actuator has a first group of components interlinked to the valve piston which cyclically move the valve piston between an open and a closed position in response to turning of the engine camshaft. The valve actuator also has a second group of components interlinked to the valve piston which shift the path of travel of the valve piston away from the outlet end of the valve sleeve in response to power increasing movements of the acceleration control of the engine and which shift the path of travel towards the outlet end in response to power decreasing movements of the acceleration control.
In another aspect the invention provides an internal combustion engine having at least one main piston that reciprocates within an engine cylinder, a fuel inlet valve through which fuel is admitted to the engine cylinder and an acceleration control which is movable in one direction to increase the power output of the engine and movable in an opposite direction to decrease the power output of the engine. The fuel inlet valve is a piston valve having a valve chamber with an outlet end which opens into the engine cylinder and having at least one fuel inlet port in a sidewall of the valve chamber at a location which is spaced away from the outlet end of the chamber. The inlet valve has a valve piston which is movable towards the outlet end of the chamber and away therefrom. The valve piston is movable along a path of travel which includes a first range of valve positions at which fuel flow through the inlet port is increasingly restricted by the piston and further includes a second range of valve positions at which flow through the inlet port is fully blocked by the piston and the piston becomes progressively closer to the outlet end of the valve chamber. Valve actuating components which are coupled to the valve piston include a first group of components that position the valve piston within the first range of valve positions during fuel intake strokes of the power piston and which position the valve piston within the second range of valve positions at other stages of the engine operating cycle. The valve actuating components further include a second group of components which shift the path of travel of the valve piston in response to movement of the engine acceleration control, the path of travel being moved away from the outlet end of the valve chamber in response to movement of the acceleration control in the one direction and being moved towards the outlet end in response to movement of the acceleration control in the opposite direction.
In still another aspect, the invention provides a fuel inlet valve system for an internal combustion engine having at least one power piston which reciprocates in an engine cylinder and having an acceleration control which is movable in a first direction to increase the power output of the engine and which is movable in an opposite direction to decrease the power output of the engine. The fuel inlet valve has a valve chamber with an outlet end which opens into the engine cylinder and which has a fuel inlet port at a location in the chamber that is spaced away from the outlet end. The inlet valve also has a valve piston in the chamber which is movable along a path of travel which extends towards the outlet end of the chamber, the valve piston being movable away from the outlet end through open positions which provide a progressively larger flow path from the inlet port to the outlet end and being movable towards the outlet end to closed positions at which fuel flow from the inlet port to the outlet end is blocked by the valve piston and the valve piston becomes progressively closer to the outlet end. The system further includes first valve actuator means for cyclically moving the valve piston between an open position which enables fuel flow from the inlet port to the engine cylinder and a closed position at which fuel flow is blocked. Second valve actuator means move the path of travel of the valve piston away from the outlet end in response to movement of the acceleration control in the one direction and move the path of travel of the valve piston towards the outlet end in response to movement of the acceleration control in the opposite direction.
The invention provides fuel inlet valve structure and valve operating components which vary several engine operating characteristics to provide for high fuel efficiency throughout the full range of engine power output. The fuel inlet valve controls the flow of air/fuel mixture to vary the power output or speed of the engine. This eliminates any need for a throttle valve and its attendant power losses. The inlet valve also acts to vary the compression ratio and the expansion ratio within the engine cylinder as a function of engine load to provide high fuel efficiency throughout the full range of engine loads. In the preferred form, the inlet valve also varies the effective squish area at the top of an engine cylinder in response to changes of engine load to further optimize performance. The invention provides still other advantages which will hereinafter be described.
The invention, together with further objects and advantages thereof, may be further understood by reference to the following detailed description of the invention and by reference to the accompanying drawings.